1. Technical Field
Described herein is a random number generation apparatus.
2. Related Art
Conventionally, a random number generation apparatus using a physical random number generation source is known. As its representative random number source, a thermal noise, a quantum effect, or charge traps can be mentioned. As for charge traps, there are various forms such as charge traps naturally formed by lattice defects, impurities or the like, and charge traps artificially formed by quantum dots or the like. Furthermore, the charge traps can be applied to the case where natural decrease of charges from a NAND type flash memory is utilized. The charge traps tend to be more remarkable as an element becomes finer.
On the other hand, an arithmetic random number generated by a definite algorithm has been conventionally used as a random number of a random number generation apparatus mounted on a small-sized portable terminal such as an IC card. As a high security level is demanded, its criterion becomes severe from year to year and a random number having a higher degree of genuineness is demanded.
In addition, it is becoming an indispensable condition to periodically check a quality of the random number generated by the mounted random number generation apparatus. For example, in AIS (Application notes Interpretation of the Scheme) 31 presented by Schindler et al., the on-line test, start-up test and the like are imposed on a random noise generation element.
On the other hand, a self-test type random number generation apparatus incorporating a test circuit which periodically checks the quality of the random number is known (see, for example, U.S. Patent Application Publication No. 2005/0123471). In the random number generation apparatus described in U.S. Patent Application Publication No. 2005/0123471, a random noise generation element utilizing the traps is used, a monobit test is adopted as the test method, and a random noise generation element which has produced a better result satisfying a criterion is selected out and used for random number generation.
Furthermore, a random number generation apparatus described in U.S. Patent Application Publication No. 2007/0276890 utilizes the fact that time for discharging charge stored in traps in a random noise generation element becomes random and adopts a method of assigning “1” or “0” according to whether the time taken to emit charge is longer or shorter than some reference time.
In the random noise generation element utilizing the traps, however, the charge stored in the traps tends to remain stored as described later. Even if a fixed reference value is set, the average value of the charge emission time also changes according to the number of times of use and the frequency of use. Thus, there is a possibility that it will become impossible to generate a random number of high quality having unpredictability and nonreproducibility as a physical random number.